Append4 final

@pchiusano @fthomas @radekm 

I have created the pull request and as we expected is quite a massive one :-(

Anyhow on wiki are the release notes which I think has to be updated, I just wrote some of the stuff in. 
Lets review this and when we will be ok with whats in we just can do final formating and merge. 

Also notably, the tests are passing :-)

P.

Well there is reason why dequeueOne is not here. This is related to task interruption behaviour, that would cause tasks that were interrupted to steal the `A` from the newly registered dequeuers. I don't think so we can implement dequeueOne before we will know how to correctly interrupt task and notify queue about the fact that task has been interrupted. I am sure this is solvable, but will require more thinking. 

please look on here (commit where I have discovered that issue) https://github.com/scalaz/scalaz-stream/commit/42ae5bad1be56c9a2a95c05fc8c98f2118387a3c